Calcium control of waveform in isolated flagellar axonemes of chlamydomonas

The effect of Ca(++) on the waveform of reactivated, isolated axonemes of chlamydomonas flagella was investigated. Flagella were detached and isolated by the dibucaine procedure and demembranated by treatment with the detergent Nonidet; the resulting axomenes lack the flagellar membrane and basal bodies. In Ca(++)-buffered reactivation solutions containing 10(-6) M or less free Ca(++), the axonemes beat with a highly asymmetrical, predominantly planar waveform that closely resembled that of in situ flagella of forward swimming cells. In solutions containing 10(-4) M Ca(++), the axonemes beat with a symmetrical waveform that was very similar to that of in situ flagella during backward swimming. In 10(-5) M Ca(++), the axonemes were predominantly quiescent, a state that appears to be closely associated with changes in axomenal waveform or direction of beat in many organisms. Experiments in which the concentrations of free Ca(++), not CaATP(--) complex were independently varied suggested that free Ca(++), not CaATP(--), was responsible for the observed changes. Analysis of the flagellar ATPases associated with the isolated axonemes and the nonidet- soluble membrane-matrix fraction obtained during preparation of the axonemes showed that the axonemes lacked the 3.0S Ca(++)-activated ATPase, almost all of which was recovered in the membrane-matrix fraction. These results indicate that free Ca(++) binds directly to an axonemal component to alter flagellar waveform, and that neither the 3.0S CaATPase nor the basal bodies are directly involved in this change.     

Male dominance status,female choice and mating success in the brown lemming, Lemmus trimucronatus

The objective of this study was to determine whether female brown lemmings would selectively mate with dominant conspecific males. In dyadic encounters, oestrous females paired with dominant males engaged in more frequent lordosis and contact social behaviours than those paired with subordinate males. However, the mount and thrust scores of dominant and subordinate males did not differ significantly. When females had simultaneous access to tethered dominant and subordinate males, they spent more time in close proximity to dominant males and avoided contact with subordinate males. Copulation scores were higher with dominant males. In triadic encounters with free-moving dominant and subordinate males, oestrous females spent more time near, and engaged in more sexual behaviour with, dominant males. Intermale agonistic interactions resulted in ‘privileged access’ to females by dominant males. Sexual behaviour scores were lower and there was a 10-fold increase in intermale aggression in triadic encounters between females and unfamiliar dominant and subordinate males. Both intermale agonistic interactions and female ‘choice’ behaviour accounted for the differential copulatory success of dominant males.     

Presynaptic Inhibition by Concanavalin A: Are α-Latrotoxin Receptors Involved in Action Potential-Dependent Transmitter Release?

Abstract: Effects of concanavalin A on transmitter release were investigated in primary cultures of chick sympathetic neurons. The lectin reduced electrically evoked [³H]noradrenaline release by up to 30% with half-maximal inhibition at 0.16 µ M . Concanavalin A also reduced the release triggered by extracellular Ca²⁺ in neurons depolarized by 25 m M K⁺ or rendered Ca²⁺-permeable by the ionophore A23187. The inhibitory action of concanavalin A on electrically evoked release was additive to that of the α₂-adrenergic agonist UK 14,304. Inactivation of G_s and G_i/G_o type G proteins by either cholera or pertussis toxin did not alter the inhibitory effect of the lectin. Concanavalin A failed to affect the resting membrane potential, action potential waveforms, or voltage-dependent K⁺ and Ca²⁺ currents. In contrast, the lectin efficiently blocked both the Ca²⁺-dependent and -independent α-latrotoxin-induced transmitter release, but only when applied before the toxin. The reduction of electrically evoked, as well as α-latrotoxin-evoked, release by concanavalin A was attenuated in the presence of glucose and abolished by methyl α- d -mannopyranoside. The dimeric derivative, succinyl-concanavalin A, was significantly less active than tetrameric concanavalin A. In bovine adrenal chromaffin cells, which displayed only weak secretory responses to α-latrotoxin, concanavalin A failed to alter K⁺-evoked catecholamine secretion. These results show that concanavalin A causes presynaptic inhibition in sympathetic neurons and indicate that cross-linking of α-latrotoxin receptors may reduce action potential-dependent transmitter release.     

Histiostoma papillata sp. n. (Acari: Histiostomatidae), a mite attacking fish in Australia

Histiostoma papillata sp. n. (Acari: Histiostomatidae) is described from Victoria, Australia. It was found in the fins and gills of juvenile Murray cod, Maccullochella peelii peelii (Mitchell), where it appeared to inflict injuries thought to be responsible for the mortality of fish in a diet trial.     

Modulation of spontaneous and stimulation-evoked transmitter release from rat sympathetic neurons by the cognition enhancer linopirdine: insights into its mechanisms of action

The mechanisms by which the cognition enhancer linopirdine may affect transmitter release were investigated in cultures of rat superior cervical ganglion neurons. Overflow of previously incorporated [3H]noradrenaline evoked by 10 microM UTP or 0.1 microM bradykinin was enhanced by linopirdine at > or =3 microM, overflow evoked by 25 mM K(-), 100 microM nicotine, or 300 microM ATP was enhanced by linopirdine at > or =10 microM, and overflow due to 40 mM K+ or electrical field stimulation was not altered by linopirdine. Ba2+ (0.3 mM) augmented the same types of stimulation-evoked overflow to a similar extent as linopirdine. K+ (25 mM), nicotine (100 microM), and ATP (300 microM) triggered transmitter release in a partially tetrodotoxin-resistant manner, and the release-enhancing action of linopirdine was lost in the presence of tetrodotoxin (1 microM). Linopirdine (10 microM) raised spontaneous tritium outflow and reduced currents through muscarinic K+ (K(M)) channels with a similar time course. The secretagogue action of linopirdine was concentration- and Ca2(+)-dependent and abolished by tetrodotoxin (1 microM) or Cd2+ (100 microM). Linopirdine (10 microM) added to the partial inhibition of K(M) channels by 1 or 3 mM Ba2(+) but not to the complete inhibition by 10 mM Ba2(+). Likewise, the secretagogue action of 1 and 3 mM, but not that of 10 mM, Ba2+ was enhanced by linopirdine. These results indicate that linopirdine facilitates and triggers transmitter release via blockade of K(M) channels and suggest that these K+ channels are located at neuronal somata rather than at presynaptic sites.     

Range-wide phylogeography of the European temperate-montane herbaceous plant Meum athamanticum Jacq.: evidence for periglacial persistence

Aim  The aim of this study is to analyse the genetic population structure of Meum athamanticum Jacq. in order to explore the alternative hypotheses (1) that the central and northern highland populations are the result of post-glacial recolonization from southern refugia, and the disjunct distribution of M. athamanticum can be explained by modern ecological conditions, or (2) that extant populations north of the Alps and Pyrenees persisted in situ during glacial periods.
Location  Europe.
Methods  Variation of amplified fragment length polymorphisms (AFLPs) was analysed for 23 populations from the entire range of the species. We used band-based approaches and methods based on allele frequencies to measure genetic diversity and to identify population structure.
Results  Our analyses reveal a north–south differentiation within M. athamanticum . High levels of genetic diversity, as well as private fragments, are found in populations both north and south of the Alps. Differentiation among populations is lower in the northern than in the southern population group, and significant isolation-by-distance is found only in the latter group.
Main conclusions  Our results indicate that M. athamanticum survived the last ice age in multiple refugia throughout its contemporary range and did not expand into areas north of the Alps from southern refugia. We found evidence that regional-scale migration in northern, formerly periglacial, parts of the species range has resulted in the intermingling of populations. In contrast, southern populations are characterized by long-term isolation. The south-west Alps represent an area where immigration and mixing of populations from northern and southern refugia appears to have taken place.     

Near infrared spectroscopy compared to liquid chromatography coupled to mass spectrometry and capillary electrophoresis as a detection tool for peptide reaction monitoring

Peptide interaction is normally monitored by liquid chromatography (LC), liquid chromatography coupled to mass spectrometry (LC-MS), mass spectrometric (MS) methods such as MALDI-TOF/MS or capillary electrophoresis (CE). These analytical techniques need to apply either high pressure or high voltages, which can cause cleavage of newly formed bondages. Therefore, near infrared reflectance spectroscopy (NIRS) is presented as a rapid alternative to monitor the interaction of glutathione and oxytocin, simulating physiological conditions. Thereby, glutathione can act as a nucleophile with oxytocin forming four new conjugates via a disulphide bondage. Liquid chromatography coupled to UV (LC-UV) and mass spectrometry via an electrospray ionisation interface (LC-ESI-MS) resulted in a 82% and a 78% degradation of oxytocin at pH 3 and a 5% and a 7% degradation at pH 6.5. Capillary electrophoresis employing UV-detection (CE-UV) showed a 44% degradation of oxytocin. LC and CE in addition to the NIRS are found to be authentic tools for quantitative analysis. Nevertheless, NIRS proved to be highly suitable for the detection of newly formed conjugates after separating them on a thin layer chromatography (TLC) plate. The recorded fingerprint in the near infrared region allows for a selective distinct qualitative identification of conjugates without the need for expensive instrumentation such as quadrupole or MALDI-TOF mass spectrometers. The performance of the established NIRS method is compared to LC and CE; its advantages are discussed in detail.     

Abnormal DNA methylation and deoxycytosine-deoxyguanine content in nucleosomes from lymphocytes undergoing apoptosis.

Systemic lupus erythematosus (SLE) is characterized by an accelerated apoptosis of peripheral lymphocytes and an impairment of the clearance of apoptotic cells. Since changes in DNA methylation and in deoxycytosine and deoxyguanine (GC) content have been shown to enhance the potential of DNA to activate murine and human B lymphocytes, we tested the capacity of lymphocytes undergoing apoptosis (under conditions that mimic the deletion of self-reactive cells after antigen receptor engagement) to generate nucleosomes with a particular base composition. Using two cell culture systems and four apoptosis triggers, we found an increase of deoxymethylcytosine in fragmented chromosomal DNA of apoptotic B and T lymphocytes. However, this increase was not associated with modulation of DNA (cytosine-5) methyltransferase, the enzyme that methylates eukaryotic DNA, which suggests that the changes in DNA methylation patterns are not linked to the process of de novo DNA methylation during cell death. In addition, we could not detect a unique methylation pattern in highly repetitive Alu sequences present in the human genome of SLE subjects, as compared with controls. However, the abnormal DNA methylation of apoptotic nucleosomes was associated with an unusual pattern of nuclease-resistant, GC-rich regions in these DNA fragments. We propose that the combination of an accelerated apoptosis with a defect in the clearance of apoptotic cells results in release of increased amounts of nucleosomes with abnormally methylated, GC-rich DNA and provides an autologous stimulation that could bypass tolerance to self in systemic autoimmune diseases. These findings support the concept that the structure and dynamics of nucleosomes are critical in determining their immunogenicity in SLE.